This invention relates to a method of bending a glass plate, and more particularly to an improved way of heating the glass plate to be bent. For example, the glass plate is bent to produce a building or vehicle window glass.
Bent glass plates are largely used as window glasses in recent buildings and automobiles and some other vehicles, and there is an increasing demand for bent glass plates of beautiful appearance. However, when a glass plate is bent to a large curvature it is often that images reflected in end regions of the bent glass plate are conspicuously distorted. An important cause of the distortion of the reflected images is local irregularities of the convex or concave surface of the bent glass plate and in particular local concavities in the convex surface. In general optical distortion of a bent glass plate augments as the glass plate is thicker and as the bent glass plate has a smaller radius of curvature.
With a view to preventing optical distortion of glass plates bent, e.g., by a press bending method or a sag bending method there are various proposals of modifying the configuration of the bending mold(s) or the manner of engagement of the heated glass plate with the mold(s). Besides, there are some proposals of nonuniform heating of a glass plate to be bent. For example, JP-A 56-22643 relates to intensified heating of a glass plate along the line of relatively sharp bend by using a heater strip printed on the glass plate along the intended bend line and proposes to form the heater strip in a curved pattern for the purpose of shaping the glass plate to a desired curvature on each side of the sharp bend line. On the other hand, JP-A 62-56327 proposes to weaken the heating of a nearly rectangular glass plate, which is to be bent by a sag bending method, in two opposite end regions along the longer edges of the glass plate by detachably applying a heat reflective coating to the glass surface in each of the end regions.
However, in the case of bending a relatively thin glass plate such that the bent glass plate has a radius of curvature not larger than 2000 mm or in the case of bending a glass plate not thinner than 6 mm so as to have a radius of curvature not larger than 3000 mm, the measures hitherto proposed are not fully effective for preventing the distortion of images reflected in end regions of the bent glass plate. In particular, when a nearly rectangular glass plate is bent such that two opposite edges of the glass plate become curved it is likely that images reflected in end regions of the bent glass plate along the other edges are considerably distorted.